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          <h1 class="post-title" itemprop="name headline">flash 和 ram 的映像分布</h1>
        

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        <p>在上一篇文章聊iap的时候，没有对flash分区进行展开说，这一篇文章，聊一下arm-cortex系列Flash和Ram的分区，也算是对上一篇文章的部分内容的一个呼应吧。</p>
<a id="more"></a>

<hr>
<h1 id="Flash和Ram里究竟是什么？"><a href="#Flash和Ram里究竟是什么？" class="headerlink" title="Flash和Ram里究竟是什么？"></a>Flash和Ram里究竟是什么？</h1><p>程序在编译后会生成一个.map文件，该文件是在链接过程中生成的，指示了ram和rom(flash)的映像分布以及使用情况，所以就先从.map文件来看一下flash和ram的数据分布情况。<br>下面是STM32F407的一个rom映像文件(删去了部分重复区域数据)。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line">  Load Region LR_IROM1 (Base: 0x08000000, Size: 0x0000bbbc, Max: 0x00100000, ABSOLUTE, COMPRESSED[0x0000b9fc])</span><br><span class="line"></span><br><span class="line">    Execution Region ER_IROM1 (Exec base: 0x08000000, Load base: 0x08000000, Size: 0x0000b984, Max: 0x00100000, ABSOLUTE)</span><br><span class="line"></span><br><span class="line">    Exec Addr    Load Addr    Size         Type   Attr      Idx    E Section Name        Object</span><br><span class="line">#section 1: RESET</span><br><span class="line">    0x08000000   0x08000000   0x000001ac   Data   RO         1975    RESET               startup_stm32f429xx.o</span><br><span class="line">#section 2: CODE    </span><br><span class="line">    0x080001ac   0x080001ac   0x00000008   Code   RO         5266  * !!!main             c_w.l(__main.o)</span><br><span class="line">    0x080001b4   0x080001b4   0x00000034   Code   RO         5435    !!!scatter          c_w.l(__scatter.o)</span><br><span class="line">    0x080001e8   0x080001e8   0x0000005a   Code   RO         5433    !!dczerorl2         c_w.l(__dczerorl2.o)</span><br><span class="line">#section 3: constdata    </span><br><span class="line">    0x08009e02   0x08009e02   0x00000014   Data   RO          113    .constdata          components.o</span><br><span class="line">    0x0800b940   0x0800b940   0x00000024   Data   RO         3472    FSymTab             msh_cmd.o</span><br><span class="line">    0x0800b964   0x0800b964   0x00000020   Data   RO         5431    Region$$Table       anon$$obj.o</span><br></pre></td></tr></table></figure>
<p>可以知道该flash基地址为0x08000000,使用了46KB,最大为1MB,flash的部分可以分为以下几段如下表。</p>
<table>
<thead>
<tr>
<th>地址</th>
<th>区域</th>
</tr>
</thead>
<tbody><tr>
<td>0x08000000~0x080001ac</td>
<td>vectors</td>
</tr>
<tr>
<td>0x080001ac~0x0800b940</td>
<td>code</td>
</tr>
<tr>
<td>0x0800b940~0x0800b964</td>
<td>constdata</td>
</tr>
<tr>
<td>……</td>
<td>未使用区域</td>
</tr>
</tbody></table>
<p>下面是STM32F407的RAM映像文件（删除了部分重复区域数据）</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line">    Execution Region RW_IRAM1 (Exec base: 0x20000000, Load base: 0x0800b984, Size: 0x00000e28, Max: 0x00030000, ABSOLUTE, COMPRESSED[0x00000078])</span><br><span class="line"></span><br><span class="line">    Exec Addr    Load Addr    Size         Type   Attr      Idx    E Section Name        Object</span><br><span class="line">#section 1:data</span><br><span class="line">    0x20000000   COMPRESSED   0x00000004   Data   RW            6    .data               clock.o</span><br><span class="line">    0x20000004   COMPRESSED   0x00000009   Data   RW          602    .data               irq.o</span><br><span class="line"> </span><br><span class="line">    0x2000022c   COMPRESSED   0x00000009   Data   RW         3569    .data               stm32f4xx_hal.o</span><br><span class="line">    0x20000235   COMPRESSED   0x00000003   PAD</span><br><span class="line">#section 2:bss    </span><br><span class="line">    0x20000238        -       0x00000190   Zero   RW          276    .bss                idle.o</span><br><span class="line"></span><br><span class="line">    0x200007c1   COMPRESSED   0x00000003   PAD</span><br><span class="line">    0x200007c4        -       0x00000060   Zero   RW         5305    .bss                c_w.l(libspace.o)</span><br><span class="line">    0x20000824   COMPRESSED   0x00000004   PAD</span><br><span class="line">#section 3:heap      </span><br><span class="line">    0x20000828        -       0x00000200   Zero   RW         1974    HEAP                startup_stm32f429xx.o</span><br><span class="line">#section 4:stack  </span><br><span class="line">    0x20000a28        -       0x00000400   Zero   RW         1973    STACK               startup_stm32f429xx.o</span><br></pre></td></tr></table></figure>
<p>可以知道RAM基地址为0x20000000,使用了3642字节，总大小为192KB,Ram的部分可以分为以下几段如下表。</p>
<table>
<thead>
<tr>
<th>地址</th>
<th>区域</th>
</tr>
</thead>
<tbody><tr>
<td>0x20000000~0x20000235</td>
<td>Data(已初始化全局变量)</td>
</tr>
<tr>
<td>0x20000235~0x20000828</td>
<td>Bss(未初始化全局变量)</td>
</tr>
<tr>
<td>0x20000828~0x20000a28</td>
<td>堆区（从20000828开始分配空间）</td>
</tr>
<tr>
<td>0x20000a28~0x20000a28+0x00000400（栈顶地址）</td>
<td>栈区（从栈定地址开始分配空间）</td>
</tr>
</tbody></table>
<p>要注意的是，堆的基地址是紧随bss段的，因次堆的基地址不固定;栈区是紧跟着堆区，栈的栈顶地址不固定。堆溢出：堆溢出之后，就会到影响到栈区的数据，栈溢出：栈溢出的话会首先影响堆的数据，然后再是bss段，再是Data段。</p>
<h1 id="什么决定了Flash和Ram的映像分布？"><a href="#什么决定了Flash和Ram的映像分布？" class="headerlink" title="什么决定了Flash和Ram的映像分布？"></a>什么决定了Flash和Ram的映像分布？</h1><p>要看是什么决定了Flash和Ram的映像分布，就得先从程序的编译过程开始了解，下图是gcc编译链开发流程模式图（arm-cc编译过程类似），从图中可以看到c文件和S文件先经由编译器和汇编器进行预编译和编译生成.o目标文件,然后经由链接器将文件生成可执行文件映像，再通过格式转换工具转换为我们需要的.bin或.hex文件。所以决定Flash和Ram映像分布的，就是链接这个过程了。</p>
<p><img src="/blog/2020/04/23/flash-and-ram/guncompiler.png" alt="asset"></p>
<p>图1：gnu编译链开发流程模式图</p>
<h2 id="分散加载"><a href="#分散加载" class="headerlink" title="分散加载"></a>分散加载</h2><p>找到keil-&gt;linker，可以看到链接是指向了一个链接脚本，找到这个脚本，发现目录下除了一个脚本文件还有一个.lds文件(这个文件是给gnu编译链用的，暂且不介绍)。</p>
<p><img src="/blog/2020/04/23/flash-and-ram/sct.png" alt="asset"></p>
<p>link.sct脚本文件是keil自动生成的，实现对各个.o文件分散加载然后合并成一个映像文件。根据target对Rom和Ram的分配自动生成链接文件。对于分散加载文件脚本的详细信息可以在《Arm Compiler 5 User’s Guide》的《linker User Guide》</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">LR_IROM1 0x08000000 0x00100000  &#123;    ; load region size_region      &#x2F;&#x2F;加载域</span><br><span class="line">  ER_IROM1 0x08000000 0x00100000  &#123;  ; load address &#x3D; execution address  &#x2F;&#x2F;加载域&#x3D;运行域</span><br><span class="line">   *.o (RESET, +First)   &#x2F;&#x2F;RESET段  放在第一个区域</span><br><span class="line">   *(InRoot$$Sections)  &#x2F;&#x2F;将所有library section放置在根区域 如__main.o, __scatter*.o, __dc*.o, and *Region$$Table</span><br><span class="line">   .ANY (+RO)    &#x2F;&#x2F;匹配所有目标文件或库ROData and ROcode</span><br><span class="line">  &#125;</span><br><span class="line">  RW_IRAM1 0x20000000 0x00030000  &#123;  ; RW data</span><br><span class="line">   .ANY (+RW +ZI)</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>注：在gnu中，分散加载通过一个.ldr或者.ld文件来实现，若要实现flash或者ram的分区，堆栈大小的指定就需要在.ld文件中设置。<br>从分散加载文件上来看，与生成的.map映射基本一致，编译器还做了其他的一些操作，但是对用户不可见，后续会通过对gcc编译过程分析时，再更加详细分析链接过程。</p>
<hr>
<h1 id="参考文献"><a href="#参考文献" class="headerlink" title="参考文献"></a>参考文献</h1><p>1、《Cortex-M3权威指南》<br>2、《Arm Compiler 5 User’s Guide》</p>

      
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